The invention relates to polycarbonates. More specifically, it relates to a method and system for preparing a polycarbonate copolymer by addition of a copolymerization reagent to a copolycarbonate. Also, the invention relates to a copolycarbonate produced by the method and system.
Polycarbonate compositions exhibit valuable mechanical properties such as impact resistance, heat resistance and transparency. The compositions are widely used in engineering applications. In certain processes and applications such as optical storage media, it is desirable to use a polycarbonate composition that is transparent and that exhibits low water affinity, good processibility, good heat resistance and low birefringence. Water affinity is particularly undesirable in a composition used as a high density optical data storage medium. Moisture can cause recording layer warpage resulting in poor data fidelity.
In a typical method for producing a polycarbonate, an aromatic dihydroxy compound such as bisphenol and a diaryl carbonate such as diphenyl carbonate are reacted in a molten state ester exchange. This method is called melt-polycondensation. A polycarbonate copolymer can be produced in a melt-polycondensation by polymerizing diphenyl carbonate and bisphenol A together with other optionally substituted bisphenols, diesters or diacids as comonomers.
In one process for producing substituted bisphenol A (BPA) based copolycarbonates, 2,2-(bis-3-isopropyl-4-hydroxyphenyl)propane is reacted together with bisphenol A and diphenyl carbonate (DPC) and tetramethyl-ammonium hydroxide (TMAH) and NaOH catalyst in a melt transesterification process. This process can require very long reaction times to obtain copolymers with even low molecular weight.
A typical melt transesterification plant utilizes overhead systems that distill off and recycle valuable phenol by-product. Recovery of BPA and DPC monomer by-product is made more difficult when the phenol recycle stream includes other monomers used to form a copolymer. The additional monomers must be separated from the recycle stream. The required separation process is complicated if the monomers have boiling points and vapor pressures similar to other recycle stream components.
Typical melt transesterification plants use a continuous process involving several reactors and polymerizers in series. Several hours can be required to obtain stable operation after a change in a feed composition in a first monomer mix tank. During this period, large quantities of variable composition transition material having ill-defined properties are produced.
There is a need for an improved process for the production of polycarbonate copolymers in a continuous melt reaction system. Additionally, there remains a need for improved processing reagents and for an improved product modified to customize a product polycarbonate for a particular use.
The invention provides an improved copolymerization process, copolymerization reagent and product. According to the invention, a method for preparing a copolycarbonate comprises preparing a (A) free hydroxyl-containing polycarbonate and reacting the hydroxyl-containing polycarbonate with a mixture of (B) a symmetrical optionally activated aromatic carbonic acid diester and (C) an optionally substituted aromatic dihydroxy compound, diol or diacid.
In another embodiment, the invention is a copolymerization reagent comprising a mixture of (B) a symmetrical optionally activated aromatic carbonic acid diester and (C) an optionally substituted aromatic dihydroxy compound, diol or diacid.
In another embodiment, the invention comprises a method for preparing a copolycarbonate, comprising reacting an (i) aromatic dihydroxy compound with a (ii) carbonic acid diester to prepare a (A) free hydroxyl-containing polycarbonate and reacting the (A) free hydroxyl-containing polycarbonate with a mixture of a (B) symmetrical optionally activated aromatic carbonic acid diester and an (C) optionally substituted aromatic dihydroxy compound, diol or diacid in a stoichiometric molar ratio of about 0.01 to about 0.75 (C) optionally substituted aromatic dihydroxy compound, diol or diacid to the (i) aromatic dihydroxy compound reacted to form the (A) free hydroxyl-containing polycarbonate.
In still another embodiment, the invention is a copolymer comprising [polycarbonate]x moieties comprising (i) aromatic dihydroxy moieties and (ii) carbonic acid diester moieties; (B) [symmetrical optionally activated aromatic carbonic acid diester]y moieties and (C) [optionally substituted aromatic dihydroxy compound, diol or diacid]z moieties wherein x is 30 to 80 mole percent, y is 10 to 35 mole percent and z is 10 to 35 mole percent of the copolymer.
In still another embodiment, the invention is a method for preparing a copolycarbonate, comprising: preparing a (A) free hydroxyl-containing polycarbonate and sequentially reacting the (A) free hydroxyl-containing polycarbonate in at least a first copolymerization and a second copolymerization with a mixture of a (B) symmetrical optionally activated aromatic carbonic acid diester and an (C) optionally substituted aromatic dihydroxy compound, diol or diacid.
A copolymer comprises (A) [copolycarbonate moieties]x comprising (i) aromatic dihydroxy moieties and (ii) carbonic acid diester moieties; (B) symmetrical optionally activated aromatic carbonic acid diester moieties; and (C) optionally substituted aromatic dihydroxy compound, diol or diacid moieties in a mole percent ratio of about 0.01 to about 0.75 of (C) optionally substituted aromatic dihydroxy compound, diol or diacid moieties to (i) aromatic dihydroxy moieties.
A system for preparing a copolycarbonate, comprises a first reactor for reacting an (i) aromatic dihydroxy compound with a (ii) carbonic acid diester to produce a copolycarbonate and a contiguous polymerizer for reacting a controlled stoichiometric mixture of a (B) symmetrical optionally activated aromatic carbonic acid diester and an (C) optionally substituted aromatic dihydroxy compound, diol or diacid with the oligomer to produce a copolycarbonate.
Finally, an optical storage media is constructed by preparing a (A) free hydroxyl-containing polycarbonate; reacting the (A) free hydroxyl-containing polycarbonate with a controlled stoichiometric mixture of a (B) symmetrical optionally activated aromatic carbonic acid diester and an (C) optionally substituted aromatic dihydroxy compound, diol or diacid to produce a copolymer; and incorporating the copolymer into an optical structure as a storage media.